Process for the acid-treating of catalytically cracked naphtha



Patented Mar. 23, 1948 PROCESS FOR THE ACID-TREATING OF CATALYTICALLYCRACKED NAPH'IHA Arnold F. Kaulakis, Roselle, N. J., assignor toStandard Oil Development Company, a corporation of Delaware ApplicationSeptember 15, 1943, Serial No. 502,440

2 Claims. 1

This invention relates to treating hydrocarbons, and more particularly,relates to acid-treating of catalytic naphthas to improve the anti-knockquality of aviation gasoline or blending stock.

It is known that certain olefins are undesirable constituents inaviation gasolines and difierent methods have been described forremoving undesirable olefins from such fractions. Some of these methodsare referred to hereinafter. It has been reported that sulfuric acidtreatment of low sulfur catalytic naphthas in the aviation gasolineboiling range results in no significant improvement in either AFD-lC andAFB-3C anti-knock quality (presently to be described), and in some casesresults in decrease in AFD-3C quality. These results apply particularlyto the sulfuric acid treatment of a total aviation naphtha in the 05-350F. range.

The AFD-lC method of evaluating aviation gasoline anti-knock quality iscarried out in accordance with Army-Navy specification AN-VV-F-746. Thisrating is designed to be a measure of the anti-knock quality of the fuelunder lean-mixture conditions such as would exist under cruisingconditions in aircraft. The rating is expressed in terms of the volumeper cent of iso-octane that must be blended with normal heptane to givea blend which will just equal the anti-knock quality of the test samplein the AFD-1C engine.

The AFB-3C rating is designed to indicate the anti-knock quality of thegasoline under rich mixture conditions such as are encountered inaircraft operations under take-off or combat operations. The rating isgenerally expressed in terms of the volume of lead tetraethyl(milliliters per U. S. gallon) that must be added to S Reference fuel(commerc al iso-octane) to match the anti-knock quality of the testsamples in the AFB-3C test engine. The rating is sometimes expressed interms of the indicated mean effective pressure (IMEP) developed in theAFB-3C test engine. The AFB-3C rich mixture testing is made according toArmy-Navy specifications AN-VV-F-748, and the rating obtained isdirectly proportioned to the maximum knock-free power of an engine usingthis fuel. Therefore, fuels of high AFB-3C quality are more desirablesince they will give more knock-free power in the aircraft engine.

I have found that by separating catalytically cracked naphtha ofrelatively high olefin content into two or more fractions and separatelytreating these fractions with concentrated sulfuric acid rather thanacid-treating the total naphtha cut, substantial increases in AFB-1C,and more particularly in AFB-3C anti-knock quality are obtained. Thetotal catalytically cracked naphtha fraction contains olefins,aromatics, naphthenes, and paraffins, and if the total naphtha fractioncontaining a large percentage of olefin-s is treated with sulfuric acid,some aromatics are lost by the alkylation of aromatics with olefins.

'If the separate fractions are acid-treated, there is less loss due toalkylation because the aromatics are concentrated in the higher boilingfraction .or fractions and the ratio of aromatics to olefins is thenunfavorable to the alkylation reaction. My improved results areapparently due to the more selective removal of olefins, the removal ofwhich results in the concentration of aromatics and naphthenes.

In addition to the possibility of acid-treating naphthas in conventionalequipment, my process can readily be installed in refineries wheresulfurie acid alkylation is practiced with a small expenditure forcontacting and rerunning.

In the drawing;

Fig. 1 represents one form of apparatus which may be used to carry outmy process; and

Fig. 2 represents another form of apparatus wherein my process may beused in a refinery which practices sulfuric acid alkylation of lowerboiling hydrocarbons.

In the catalytic cracking of relative y heavy hydrocarbons, such as gasoils. to produce lower boiling hydrocarbons. the gasoline producedcontains aromatics, olefins, naphthenes, and paraflins. The aromatics,naphthenes and branched chain parafiins are desirable constituents foraviation gasoline but olefins are generally undesirable.

,One method for removing olefins is acid-treating, which has long beenpracticed in petroleum refineries.

ever, not desirable for treating catalytically cracked fractions. Forexample, in the production of aviation gasoline, it has been reportedthat there is a loss in AFB-3C rating of the aviation gasoline if it isacid-treated with concentrated sulfuric acid. I have found, however,that if the aviation gasoline or naphtha fraction is divided into two ormore fractions, and each fraction treated separately with sulfuric acidof concentrations and acid oonsumptions optimum for each fraction, thatan actual increase in the AFB-3C rating is obtained.

There are other ways of removing olefins or separating aromatics ornaphthenes from the cracked gasoline, and my process compares favorablywith them. Other processesare catalytic after treating of thecatalytically cracked gasoline, hydrogenation of the catalytica-ll'ycrackedmv naphtha and solvent extraction of the catalytically crackednaphtha.

Referring now to Fig. 1 of theurawings. the if referencecharacter ldesignates a line for con veying catalytically cracked naphtha to afractionating tower I2 for separating the naphtha into desiredfractions. For example, a gas oil is cracked at a temperature of about925-1500 F.,opreferably 975 F. in the presence of a catalyst, such as,synthetic gels, acid-treated. bentonites, etc., preferablysilica-alumina gelcatalyst. 'The cracked naphtha is separated from'thecracked products.

Conventional acid-treating is, how- C4 and lighter are taken overhead'tower 42 as reflux liquid. The rest of the liquid 4 and condenser 46 toa liquid gas separator 52 wherein uncondensed gases and vapors areseparated from liquid. The gases or vapors pass overhead through line 54and the liquid is withdrawn from the bottom of the separator 52 throughline 56. At least a portionof the liquid withdrawn through line 56 ispassed through line 58 by pump 62 and. returned to the fractionatingfrom line 56 forms the desired lighter treated fraction and will bereferred to hereinafter.

Bottoms from the fractionator 42 are withdrawn through line 64. Thesebottoms contain higher boiling constituents in thegasoline'boiling'range and may be used as blending agents for ordinarymotor gasoline.

The 225 to 350 F. fraction is given a similar treatment though theoptimum treating condithrough line [4 and may be sent to storage or whenthe composition of these fractions is given.

However, both fractions contain olefins and it is preferred toacid-treat both of the fractions.

The C5 to 225 F. fraction is introduced into an acid-treating tank 24provided with a stirrer26,

or other suitable means of providing intimate contact between acid andnaphtha. Concen- A heavier fraction having a boiling,

tions may differ from those for thelight fraction.

The 225-350 F2. fraction is passed to an acidtreating tank 65 providedwith a stirrer 68 or other meansof providing required mixing.Concentrated sulfuric acid having a concentration of about 85 to 98% isintroduced into the tank 6 6 through line i2 and after sludge iswithdrawn through line 14. The amount of sulfuric acid 1 used is about 5to 60 pounds per barrel of oil fraction treated, dependingon acidstrength, the olefin content of the fraction, etc. v of mixing andreaction in the acid tank 55' is from about2 to 120 minutes,longer timesbeing usedwith weaker acid. The temperature during treating is about 30?F. to 120 F. a 7

The acid-treated225 to 3'50 F. fraction is then passed through line T5to another wash tank 18 where the fraction is washed with alkaline waterto remove entrained acid. The washed 225- 350 F. fraction is'then passedthrough line 82 to V a second fractionating tower 84"for recovering thedesired-treated fraction. 'Instead' of using two fractionators 42* and8d for the separate fractions, the fractions may be: combined andfractionated in one fractionator. H V V As above pointed out, theheavier fraction also contains olefins and the acid; treatment removes alarge part of the olefins. In the fractionating tower 84 the treated:heavier fraction is heated and fractionated to separate a desired 225 to350 F. fraction. Higher boiling constitutrated sulfuric acid having aconcentration of 7 about 85 to 98% is introduced into the tank 24through line 28 and acid sludge is withdrawn through line 32. The amountof acid used may vary between about 5 to 60 pounds of sulfuric acid perbarrel of oil treated, depending on the olefin content of the naphtha,vthe improvement desired, and the strength of acid that is to'be used intreating. Preferably, about 20 to 30 pounds of sulfuric acid (98%) perbarrel of oil is used. The temperature may vary between about 30 to 120F. V

The time of contact of the acid and'the oil fraction is from 2 to 120minutes, longer times being used with weaker acid. The acid treatmentremoves a large part of the olefins and the treated C5 to 225 F.fraction is withdrawn through. line 34 and passed through a wash tank 35where the fraction is Washed with alkaline water to remove entrainedacid. The Washed fraction is then passed through line 381:0 afractionating. tower 42 for rerunning. the treated fraction.

' The desired volatile fraction passes overhead from the fractionatingtower 42 through line 44 cuts are drawn off 'asbottom'sthroughline andmay be used as blending agents for ordinary motor gasoline.

The vapors pass overheat from the fractionating tower 84' through line86 and condenser 88 to a liquidgas separator 92 for separating liquidsfrom gases and vapors. The gases and vapors pass overhead throughlineo94. .The liquid is withdrawn from the bottom of the separator 92through line'9B and at least a portion thereof is passed through line 98by pump [02 and returned to the top of the fractionating tower 84 asreflux liquid. The rest of the liquid. is passed through line I04 andcombined with the. treated lighter fraction passing through line I06which forms a continuationof line 56. The combined naphtha fractions arewithdrawn from. the system through.

line M8. The combined treated naphtha fraction has a higher AFD-IC and ahigher AFB-3C rating than the totalnaphtha fraction. would,

have if acid-treated as a single fraction.

The following datairepresent one example to line fractions containingsubstantialproportions of olefins and aromatics:

The time Table 1.Acid treated fractions compared with acid treated totalnaphtha Treating uality Increase gfig Ioss Vol. l'limg of Q er cen reamg Decrease on Feed AFD-lO AFB-30 1 HeS0498% l#/Bbl. of Oil Treated:Minutes (ls-225 F 23 1 3 3. 3 8.1 225-350 F 7 6. O 3 3. 5 12. 7

Total Recombined 10. 5 3. 4 10. 0

Treat Cu350 F. (Total) 10# HzSO4 98%/Bblof Oil 9.0 3 1.8 -l. 6

H2SO198% #/Bbl. of Oil Treated:

Oe- 225 F 46 28 3 6.3 15. 7 12 11 3 5. 0 25. 5

Total Recombined 17 3.8 19 7 Treat Ct350 F. (Total) 20# H2SO4-98%/Bbl.'

of Oil 14. 0 3 3. 3 -3. 6

1 Ratings based on fuel containing 4 ml. TEL/gal.

The above table discloses data to show that there is a quality increasein the aviation naphtha when the naphtha is divided into two fractionsand each fraction separately acid-treated. These data show that thetotal recombined naphtha after separate acid-treating of the fractionshas a much greater AFD-lC increase than the total naphtha C6 to 350 whenit is acid-treated as a single fraction. These data further show thatthere is an increase in AFB-3C rating when the fractions are separatelytreated whereas when the total naphtha fraction is acid-treated as asingle fraction there is a decrease in AFB-3C rating,

Table 2.-Composition 0f fraction-vol. percent composition of such anaphtha is given in Table 2. A catalytically cracked gasoline of thistype having a boiling range of about 100-335 F. has and AFB-3C rating atabout 170-180 IMEP.

Only one example of catalytically cracked naphtha has been given and itis to be understood that the amounts of the different constituents mayvary with different feed stocks and different cracking conditions, suchas temperature, time of cracking and amount and kind of catalyst used,but it is generally true that the amount of olefins in the lighterfraction is greater than in the heavier fraction and the amount ofaromatics in the lower boiling fraction is much less than the amount ofaromatics in the higher boiling fraction.

The amount of improvement to be gained in Aromat- Naph- Ole- BromineFmctwn ics themes fins Pamfins No. treating the naphtha fractions varieswith the amount of acid employed as well as the strength gt-225:1? 3rig-2g of the acid. The following Table 3 discloses the 2 effect of acidquantity on the light and heavy TotalFractiOn 36 7 3 -75 naphthafractions when treating with 98% 50 strength used:

Table 3 VOL Quality Improvement Treating Number AFD-lC IMEP Minutes225-350 2o 11 12 s. o 25. 5

1 Rating with 4 cc. tetraethyl lead added to samples.

Table 2 discloses a typical composition of catalytically crackedgasoline. Paraflinic gas oil having an A. P. I. gravity of 315 and a midboiling point of 650 F. was cracked at a temperature of about 975 F. inthe presence of synthetic silica alumina gel at about conversion, whichmeans that about 65% of the original gas oil is converted to gas, cokeand gasoline, and that there is 35% cycle oil left. Cracked naphtha isFrom the above Table 3 it will be seen that with the more drasticsulfuric acid treats greater improvement in the AFD-lC and AFB-3Cratings is obtained but at the same time greater loss of feed results.Table 3 also illustrates that the quality improvements to be gained, atfixed treating conditions, vary, depending on the boiling range and/orcomposition of the naphtha; thus, to obtain a given overall qualityimprovement my separated from the cracked, products and the .75 processof treating selected fractions is also a WWWUIOOW more efiicient schemefrom a standpoint of acid consumption and treat severity inasmuch aseach and. butenes.

fraction can be treated separately more efiecbutane/olefin'ratio of250/1.

V The C and C5 alkylate and pentanes are with.-

Table 4.E17ect of given acid treat on oarious fractzons o 1 i 11 o k 1 Lt d ata yt ca y me e ig an Naphtha Fraction Lght Heavy Total HeavyRecombined Treat# of acid /Bbl. of

Fraction 20 20 20 20 Bromine No. Decrease. 46 '12 28 Loss. Vol. Percentt 28 11 17 20 AFD-lC Improvement. 6.3 5.0 3.8 5. 7 AFB-3O IMEPImprovement 15. 7 25. 3 4. 7 20. 0 Loss/AFD-IC Improvement 4. 5 2. 2 4.5 3. 5 Loss/AFD-3C IMEP 1111-; r I

provement 1. 8 0. 4 l. 0

1 4. 2 Negative.

Crfraction contains normal butane and isobutane Isobutane from anextraneous source may be added if desired. The C4 and Cs fractions arecombined and passed through line I34 to an acid alkylation unit I36where the mixture is treated with sulfuric acid having a.

concentration of about 98%. The sulfuric acid is introduced into theunit I36 through line I38.

The temperature during alkylation is about 40 F. The alkylation iscarried out at an internal isodrawn through line I42.

7 The spent acid having a concentration of abou V 85 to 95% is withdrawnthrough line ld l'and may be used in acid-treating the Q5 to 225? F. cut(or C6 to 225 F.) and the 225 to 350 F. Or the spent acid may be passedthrough an acid recoveryunit M6 for concentrating the acid to thedesired concentration for reuse and recycling to the alkylation unitI36. 7. f r V V The C6 to 225 F. fraction is withdrawn from unit I22through line I48 and passed to an acidtreating unit I52 where it ismixed with spent acid introduced through line I5 3. The spent acid ispart of the acid leaving the alkylation. unit through line HM. Ifdesired, fresh acid may be introduced into line I54 through line I56..Ihe acid tank I52 is provided with a stirrer such as shown in'Fig. 1 orother stirring means for intimately contacting the light fraction andthe sulfuric acid. When using a weaker acidof 85 to 95% concentration,the amount of acid to light fraction may be about 20 to 100 lbs./bbl..oflight fraction. The temperature during the Table 5.-Acz'd treat forsubstantially complete olefin removal o s. 1. Highlunsaturated naphthairom 975? F., 65% conversion cracking of heavy Tinsley gas 01 2. Lowunsaturate gas oil, using higher catalyst to oil'ratio than for the 65%conversion.

A typical application of my process in a refinery producing aviationgasoline is illustrated in 2. Referring now to Fig. 2 of the drawings,

the line I20 designates a line for conducting a heavy oil stock, such asgas oil, to a cracking unit for the Production of lower boilingconstituents including gasoline. The cracking unit is diagrammaticallyshown at I22 and also includes means for separating the reactionproductsinto desired fractions. The gas oil or other stock is cracked in thepresence of powdered catalyst having a size of about 200 tov 400standard mesh or finer. The catalyst may be acid-treated bentond naphthafrom 975 F., 80% conversion cracking of heavy Tinslcy treatment is aboutF. to 120 F. and the time of contact is about 6 minutes to 60 minutes.

The acid-treated C6 to 225 fraction is withdrawn through line I 58 andis preferably given an alkaline wash (not shown in Fig. 2) and thenreiteor synthetic. silica-alumina or silica magnesia gel. Thetemperature during cracking is about 825 to I000 F. The amount ofcatalyst to liquid oil by weight is in the ratio of from about 2/1 to20 1. 7

Gases are taken overhead through line I25 and bottoms are withdrawnthrough line I25. A Q4 fraction, is Withdrawn through line I28 and a C5fraction iswithdrawn through line I32. The

run to remove light and heavy ends. The resulting C6 to 225 F. fractionhas an improved AFB-1C and AFB-3C rating as above pointed out in thedescription of Fig. 1 andthe data included in connection therewith.Spent acid from the acid tank 152 is withdrawn through line I62 and maybe recycled to the acid recovery unit I46 through line I44. Part of thespent acid may be withdrawn through line I52. I

The heavier fraction (225 to 350 F.) from unit I22 is passed throughline I56 to another aci'dtreating tank Iiit'i where it is mixed withacid introduced through line I22. The acid comprises the spent acid fromthe .alkylation unit I36 and 7 may include fresh acid introduced throughline 555.. The acid-treating tank I68 may be provided with any desirablestirring means for mixing the heavier fraction and the sulfuric acid.The sulfuric acid has a concentration of about 85 to 95%. About 20 to100 pounds of acid are used per barrel of heavy fraction. The time oftreating is about 6 to 60 minutes and the temperature during thetreating is about 60 to 120 F. Spent acid is Withdrawn through line I'Mand returned to the acid recovery unit 55 for reconcentrating thesulfuric acid.

The acid-treated 225 to 350 fraction is with drawn from theacid-treating unit E08 through line I76 and is preferably given analkaline wash to remove entrained acid and rerun to remove light andheavy ends. The treated heavier fraction has an increased AFB-1C andAFB-3C IMEP rating as above pointed out in the description of Fig. 1 andthe data included therewith. The treated light and heavy fractions maybe combined and further processed in one system including afractionator.

Instead of passing the 225 to 350 F. fraction through the acid-treatingunit 100, in some'cases it may be used as such without acidetreating. Insuch case, the heavier fraction is icy-passed around the acid-treatingunit or tank I68 through line I78 and used as such in the final product.

The final product is formed by combining the acid-treated 225 to 350 F.fraction, the acidtreated C6 to 225 F. fraction, the alkylate passingthrough line I42 and an extraneous natural base passing through lineI02. The final product in one specific case has the followingcomposition but it is understood that this is given by Way of exampleonly as the final product will vary with the quality and nature of thefractions:

Per cent by volume Cs-225 F 12.7 225 F.-350 F. 17.0 Pentanes in alkylate11.7 C4 and C5 alkylate 40.2 Natural base 18.4

The combined product is withdrawn through line I84 and has an AFD-BCrating of 203 IMEP. The extraneous natural base may have the followingcomposition:

The extraneous natural base has a boiling range of about 100 F. to 200F. and has an AFD3C rating of 140-170 IMEP.

Since aviation gasoline is an extremely high grade product, there doesexist a supply of readily available natural base stocks, so-calledmarginal bases, which are of a high quality compared to normal motorfuel, but are relatively low compared to final 100 octane aviationproduct. Since this natural base material can be obtained without theinstallation of any processes or equipment over that available in normalcrude processing, the volume of aviation gasoline can be increased bymixing this natural base with higher octane stocks, such as alkylationand/or catalytically cracked naphtha acid treated according to myinvention. The losses which accompany acid treating, although high,represent material considerably poorer than the marginal stock, and byremoving this poorer material, aviation production is increased.Further, the loss is not a complete one as the polymers recovered fromthe sul- 10 furic acid used for treating may be used in motor asolines.

Optimum treats for individual fractions are such that will eliminatesubstantially all olefins with a minimum of loss of aromatics. Splittingof the total naphtha assures the minimizing of alkylation by providingunfavorable aromatic to olefin ratios, and one advantage of splittreating results from this fact. Since the higher boiling olefins in theheavy fraction are more difiicult to remove than the olefins in thelight fraction, a more severe acid treat is required to obtain a givenquality improvement for the heavy fraction as compared to the light.

My process may be used with low or high sulfur stocks. When using myprocess for treatment of low sulfur stocks, the improvement in qualityis due primarily to the removal of olefins. Naphthas containing sulfurto the extent of about 0.20% are improved to a higher degree because ofsulfur removal in addition to the removal of olefins.

While I have specifically set forth fractions of Cs225 F. and 225 to 350F., it is to be under- I stood that the split between'the fractions mayoccur anywhere between 175 F. and 275 F., depending on the nature of thecatalytically cracked naphtha being treated. Also, more than two outsmay be made and treated, if desired.

While I have shown two forms of apparatus for carrying out my inventionand have included specific compositions, conditions, etc., it is to beexpressly understood that these are by way of example only and myinvention is not to be restricted thereto.

I claim:

1. A method of improving the IMEP of catalytically cracked aviationgasolines containing olefins and aromatics which comprises separating acatalytically cracked aviation gasoline into a (JG-225 F. fractioncontaining a major portion of the olefins and a 225-350 F. fractioncontaining a major portion of the aromatics, separately treating eachfraction with concentrated sulfuric acid having a concentration of aboutto 98% to remove olefins and then recombining the treated fractions.

2. A method according to claim 1 wherein the sulfuric acid is used inthe amount of about 5-60 pounds per barrel of fraction treated, thetemperature during treating is 30120 F. and the time of treating isabout 2 to minutes.

ARNOLD F. KAULAKIS.

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